These are impossible 90 degree overhangs. Like I said in the description, "To print without support, in Cura enable the experimental “make overhang printable” option and choose 75 degrees." This feature of Cura is able to turn the 90 degree overhang to any degree you specify by adding smaller additional support layers below the overhang to make it printable. I'm not aware of this feature available in other slicers. I think Cura is now indeed the most advanced slicer (and remains free).